Research On 3D Numerical Modeling Of Sediment Movement Under Waves And Currents

Nearly all the harbors built on coast of cohesive sediment have serious sediment siltation problem. In order to maintain water depth for the harbor basin and the channel, port management authorities have to spend massive expense not only in clearing up the depositions every year, but also in carrying out frequent water depth surveys to guarantee ship's navigation security. It is of great significance for the prediction of deposition or scouring distribution of sediment to establish a predictive mathematical model with high precision. The model can also serve to work-out dredging plan and to reduce the topographical survey frequency in some degree. It is also helpful in understanding the sediment transport inside the harbor.The basic driving forces of the coastal sediment movement are the waves, currents and their interactions. In this thesis, a preliminary predictive sendiment movement mathematical model is established to be suitable for the sediment character of Tianjin Port. The model is characterized by (1) good property in conservation since the finite volume method is used to solve the shallow water wave equation and the sediment transportation equation; (2) the mode-splitting technique is applied in the model, namely the inner mode accounting for the shear flow and the outer mode accounting for the gravity wave movement; (3) in order to fit the irregular boundary better in the natural flow, we adopted the unstructured triangular mesh for the horizontal plane andσcoordinate system for simplification of bottom and surface boundary condition in the vertical direction; (4) to sovle the current equations, the Osher's scheme with superior properties is used to compute the horizontal flux through the interface of two adjacent finite volumes, thus the model has a good property of conservation for physical quantity, up-wind property, monotonic-reserving, high resolution in capturing discontinuity, and the vertical convection terms in the scalar equations are solved by TVD(Total Variation Diminishing) scheme to enhances the the precision, and by implicit scheme to strengthen the stability. (5) the k ?εtwo-equation turbulence model, with more explicit physical meaning, is used to calculate the vertical eddy viscosity (6) dry-wet grid method is used to simulate the moving boundary in the horizontal direction so as to make the model be adaptive to mild slope topography. The model for Tianjin Harbor is calibrated by mearsured data of tide level. Sediment movement in a tide cycle is simulated. The calculated results of sediment concentration at the spring tide and ebb tide and sediment deposition in the tree typical tide cycle are presented. Topography change in a month is thus calculated by multiplying the amount of sediment deposition whithin a tide cycle by the corresponding number of days. The results of computation and the measured data agree roughly, which indicates that the present modeling has the preliminary forecast precision.Sediment movement under wave-current interaction are modeled in an assumed 3D rectangular flume with the emphasis on the effect to sediment movement by addition of waves. This part of work is believed to lay foundation for further study of sediment movement under the wave-current interaction in engineering applications.